The present invention relates to a variable high-voltage generating circuit for a light-receiving element in a receiver circuit of an optical transmission device.
When an avalanche photodiode (APD) is used as the light-receiving element in the receiver circuit in an optical transmission device, a high-voltage generating circuit is required to induce an internal amplification function in the APD.
FIG. 2 shows an example of a prior art high-voltage generating circuit for a light receiving element (such as the high-voltage generating circuit shown in Showa 61-nen Denshi Tsushin Gakkai Sogo Zenkoku Taikai Koen Ronbunshu [1986 General Meeting of the Institute of Electronics and Communication Engineers of Japan], Mar. 5, 1986, Paper No. 2485). In FIG. 2, a rectangular wave generating circuit 7 produces pulses of about 100 kHz and outputs them through an internal CMOS invertor to a switching circuit 8. A MOSFET 81 in the switching circuit 8 performs switching responsive to the above-mentioned pulses and causes the production of pulses of a large amplitude in the primary side of a transformer 9, which resonates with a capacitor 82. A constant-voltage diode 83 is provided for stabilizing the output voltage. The pulses generated in the primary side of the transformer 9 are boosted by the transformer 9, and are further boosted and rectified by a Cockcroft-Walton Circuit 4, and are then passed through a low-pass filter 5 for removal of ripple components. The filtered voltage obtained at the output of the low-pass filter 5 is used as a high-voltage power supply for a light receiving element.
In the above high-voltage generating circuit, a MOSFET and a transformer are utilized, so that miniaturization of the circuit is difficult. Furthermore, the size of the transformer is difficult to reduce, and the transformer is not suitable for mounting on a plane.